Most packaged foods are sensitive to microbial attack, especially by bacteria and fungi. Both the colour and the flavour of foods can be adversely affected as well as the amount of microbes present render the food harmful to eat. To ensure freshness and safety, foodstuffs are labelled with an expiry date or ‘best before’ date. This is arrived at empirically or by modelling the material in a laboratory. Often a safety margin is included in this estimate such that food is often thrown away when it is perfectly safe to eat. Conversely, the wrapping maybe damaged or the packing is carried out under conditions of less than expected hygiene and the food becomes unsafe quicker than the expiry label suggests.
Most current expiry dates are static and do not react to environmental changes such as temperature or moisture, which act as catalysts for microbial growth on food. At the same time, printed expiry dates are inconspicuous and often cause large amounts of food to be wasted, quite often unnecessarily.
There is art that describes the use of coloured strips inside or intimately associated with the packing that detects the presence of gases associated with decaying food. Often these measure the pH of the gas inside the packing. Higher pH gases are associated with decay. Examples of this art are shown for instance in US patent application 20040115319, others by the same inventor and US applications 20040115319 and 20120107191. These colour changing materials may be incorporated into polymers as described in US application 20120276647.
FR 2938962 A1 (Viguie Jean Pierre) discloses a device for displaying whether a temperature threshold has been exceeded, comprising a container filled with a coloured liquid which is solidified under the action of a gel, and which is transformed into a liquid state if a predetermined temperature is reached or exceeded.
U.S. Pat. No. 2,823,131 (Power) discloses a food spoilage indicator comprising a reagent and a material which changes colour when contacted with the reagent, wherein contact of the two components is delayed by freezing the foodstuff and the indicator and can be further delayed by enclosing the colour change material in a water soluble material.
There is currently no simple way for a blind and partially sighted consumer to be able to check the expiry date of foodstuffs independently as this information is only exclusively provided visually at present. Difficulties may also be faced by people with learning difficulties, children and also people who have never learned to read.